This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
BF beamforming
BS base station
BW bandwidth
CDM code division multiplexing
CRS common reference signal
CDD cyclic delay diversity
CSD cyclic shift diversity
CSI channel state information
CSTD cyclic shift time diversity
DL downlink (eNB towards UE)
eNB E-UTRAN Node B (evolved Node B)
EPC evolved packet core
E-UTRAN evolved UTRAN (LTE)
FDD frequency division duplex
HARQ hybrid automatic repeat request
IMT-A international mobile telephony-advanced
ITU international telecommunication union
ITU-R ITU radiocommunication sector
LTE long term evolution of UTRAN (E-UTRAN)
MAC medium access control (layer 2, L2)
MM/MME mobility management/mobility management entity
Node B base station
O&M operations and maintenance
OFDMA orthogonal frequency division multiple access
PDCP packet data convergence protocol
PHY physical (layer 1, L1)
PMI precoder matrix index
PRB physical resource block
RF radio frequency
RLC radio link control
RRC radio resource control
RRM radio resource management
RX receiver
SC-FDMA single carrier, frequency division multiple access
S-GW serving gateway
SNR signal to noise ratio
SRS sounding reference signal
TDD time division duplex
TX transmitter
UE user equipment, such as a mobile station or mobile terminal
UL uplink (UE towards eNB)
UTRAN universal terrestrial radio access network
XPol cross polarized
The specification of a communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently nearing completion within the 3GPP. As specified the DL access technique is OFDMA, and the UL access technique is SC-FDMA.
One specification of interest is 3GPP TS 36.300. V8.12.0 (2010-04), “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E UTRA) and Evolved Universal Terrestrial Access Network (E UTRAN); Overall description; Stage 2 (Release 8),” incorporated by reference herein in its entirety. This system may be referred to for convenience as LTE Rel-8 (which also contains 3G HSPA and its improvements). In general, the set of specifications given generally as 3GPP TS 36.xyz (e.g., 36.211, 36.311, 36.312, etc.) may be seen as describing the Release 8 LTE system. More recently, Release 9 versions of at least some of these specifications have been published including 3GPP TS 36.300, V9.9.0 (2011-12), incorporated by reference herein in its entirety, and Release 10 versions of at least some of these specifications have been published including 3GPP TS 36.300, V10.6.0 (2011-12), incorporated by reference herein in its entirety. Even more recently, Release 11 versions of at least some of these specifications have been published including 3GPP TS 36.300, V11.0.0 (2011-12), incorporated by reference herein in its entirety.
FIG. 1 reproduces FIG. 4-1 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE (not shown). The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1 MME interface and to a Serving Gateway (SGW) by means of a S1 interface. The S1 interface supports a many-to-many relationship between MMEs/S-GW and eNBs.
The eNB hosts the following functions:                functions for RRM: Radio Bearer Control, Radio Admission Control, Connection Mobility Control. Dynamic allocation of resources to UEs in both UL and DL (scheduling);        IP header compression and encryption of the user data stream;        selection of a MME at UE attachment;        routing of User Plane data towards the Serving Gateway;        scheduling and transmission of paging messages (originated from the MME);        scheduling and transmission of broadcast information (originated from the MME or O&M); and        a measurement and measurement reporting configuration for mobility and scheduling.        
Of particular interest herein are the further releases of 3GPP LTE (e.g., LTE Rel-10) targeted towards future IMT-A systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). Reference in this regard may be made to 3GPP TR 36.913, V8.0.1 (2009 03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for E UTRA (LTE-Advanced) (Release 8), incorporated by reference herein in its entirety. A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. LTE-A is directed toward extending and optimizing the 3GPP LTE Rel-8 radio access technologies to provide higher data rates at very low cost. LTE-A will most likely be part of LTE Rel-10. LTE-A will be a more optimized radio system fulfilling the ITU-R requirements for IMT-A while maintaining backward compatibility with LTE Rel-8. Reference is further made to a Release 9 version of 3GPP TR 36.913, V9.0.0 (2009-12), incorporated by reference herein in its entirety. Reference is also made to a Release 10 version of 3GPP TR 36.913, V10.0.0 (2011-06), incorporated by reference herein in its entirety.
Typical antenna deployments consist of an array of horizontally arranged antenna elements that are processed for adaptivity in the azimuth dimension. Recent architectures have been proposed for creating arrays that effectively consist of antenna elements arranged both vertically and horizontally, which therefore promise the ability to adapt in both azimuth and elevation dimensions.
The traditional systems are limited to feedback methods which do not need to know ports (antennas) are for azimuth and which are for elevation. Hence, CSI operation is inefficient due to the possibility that a large number of ports need to be sounded on all CSI-RS (or common RS) intervals. Also the total number of ports is limited by the current LTE standard (e.g., to 8). Additionally traditional systems cannot take advantage of different feedback intervals for azimuth and elevation (e.g., elevation feedback might be able to be sent less frequently than azimuth).
Many traditional systems focus on sector-specific vertical beamforming. For example, a traditional system may use the uplink of an FDD system to determine an elevation beamformer. However, this does not enable direct measurement of the elevation channel by the UE. Additionally, calibration and complex mapping between different uplink and downlink channels may be required.
Traditional pilot designs (e.g., LTE, 802.11, 802.16) are concerned with sending pilots from generic ports. Therefore, feedback cannot be tailored to elevation beamforming in addition to azimuth beamforming. This prevents efficient pilot design (e.g., traditional designs may need a complicated 12 port format). Furthermore, such pilot designs do not provide support for legacy devices.
What is needed is a technique that allows the UE to measure the azimuth and elevation channels on the downlink to facilitate both azimuth and elevation feedback.